KR0136166B1 - Treatment of waste water containing cyanide compound and oil - Google Patents

Abstract

The present invention comprises the steps of removing the heavy oil contained in the waste water by gravity in the waste water; Homogenizing the wastewater; Adjusting the pH of the wastewater to 3.5-4.5; Adding iron salt and an oxidizing agent to oxidize and remove cyan ions; And a coagulant and a polymer coagulant, and reacting with the residual iron salt, the cyan compound and the oil component to coagulate, precipitate and remove the cyan compound and oil component in the wastewater.

Description

Waste water treatment method containing cyan compound and oil

1 is a process block diagram of a cyanide compound removal method according to a conventional method.

2 is a process schematic diagram of an embodiment of a method for removing cyanide compounds according to the present invention.

3 is a graph showing the cyanide removal effect according to the H ₂ O ₂ dose in the method of the present invention

4 is a graph showing the oil removal effect according to the H ₂ O ₂ dose in the method of the present invention

5 is a graph showing the cyanide removal effect according to the pH change in the method of the present invention

6 is a graph showing the cyan removal effect according to the folding processing time in the conventional aeration method

7 is a graph showing the effect of removing cyanide compounds and oils according to the NaOC1 dose in the conventional chemical method

The present invention relates to a wastewater containing cyanide compound and an oil component, and more particularly to a coke oven gas condensate treatment method. In the coke plant, the coke oven gas (coke oven gas, hereinafter referred to simply as "COG") generated by coke distillation is transferred through pipes to be used as a heat source for each steel mill, but during the transfer, the inside and outside of the COG pipe COG condensed water is generated by the temperature difference. The COG condensate contains a large amount of high-concentration organic substances such as cyanide, tar-based oil, ammonia, sulfur, and phenol. It causes several problems. Conventionally, in order to remove such cyanide compounds and oil components in COG condensed water, COG condensed water is sent to an oil-water separation tank to remove heavy oil such as tar by gravity, and then cyanide compounds are removed from the reaction tank by using an oxidizing agent (NaOC1) in the pretreatment step. The COG condensed water from which heavy oil and free cyan were removed was sent to the wastewater treatment plant where it was mixed with other wastewater for final treatment through an activated carbon adsorption plant and a sand filer.

FIG. 1 is a schematic view of the process in which the conventional method can be implemented. COG condensate sent from the reservoir to the oil / water separation tank is where heavy oil is removed by gravity, flows into the tank, and then undergoes primary and secondary oxidation reactions in the reactor. Treated wastewater is sent to a final drainage treatment plant. In the wastewater treatment plant, the wastewater treated first in each unit and the COG condensed water treated as described above are mixed, and the final treated water is discharged through three stages of chemical reaction tank, sand filtration and carbon filter. do. However, according to the conventional method, the heavy oil is removed by gravity in the COG condensate pretreatment step, and the cyanide compound is pretreated as an oxidant in the reaction tank, but the treatment efficiency of cyanide and oil components is insufficient. Increasing pollution loads has been a major problem in wastewater treatment. Accordingly, an object of the present invention is to provide a more improved method of simultaneously removing the cyan compound and oil components contained in the COG condensed water, which solves the conventional problems as described above.

According to the present invention, in the method of treating heavy oil contained in the wastewater by gravity and then treating the homogenized COG wastewater with the cyan compound and oil, the pH of the wastewater is adjusted to 3.5-4.5 and then ferrous salt and H ₂ O Adding ₂ to generate OH radicals to oxidize cyan ions; And by administering the polymer coagulant PAA and the coagulant adjuvant Ca (OH) ₂ to the wastewater from which the cyan ions were first removed, flock was formed together with the residual iron salt and the cyan compound, and at the same time, the oil component was adsorbed to the floc to remove the cyan and oil at the same time. It comprises; a.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

When the oil component is contained in the waste water, if the waste water is treated without first removing it, problems such as deposition or accumulation of the oil component in the sewer pipe and the pump occur. Therefore, as in the prior art, the heavy oil in the wastewater is first removed by gravity from the oil-water separation tank, and then transferred to the adjustment tank to homogenize the wastewater. Then, after adjusting the pH of the wastewater introduced from the adjustment tank in the first reaction tank to 3.5-4.5, iron salt and oxidant are added to oxidize and remove the cyan ions. As the pH adjuster of waste water, acid in general, such as hydrochloric acid or sulfuric acid, may be used, but sulfuric acid is preferably used in consideration of working environment. The pH of the wastewater was adjusted to 3.5-4.5 so that iron salts and oxidants reacted to produce OH radicals easily. By adjusting the pH and adding iron salt and oxidizing agent, OH radicals are generated as shown in the following reaction formula, and the OH radicals and cyan ions react to oxidize and remove the cyan compound. As the iron salt, a monovalent iron salt oxidized to Fe ²⁺ ions such as FeCl ₂ or FeSO ₄ is used, and FeCl ₂ is preferably used as the iron salt. As the oxidizing agent, hydrogen peroxide (H ₂ O ₂ ) is preferably used in consideration of the reaction with Fe ²⁺ .

The amount of iron salt such as FeCl ₂ varies depending on the composition and concentration of the wastewater, but in the present invention, 400-600 mg / L of FeCl ₂ was used. The oxidant in consideration of the equivalent ratio between Fe ^2+, to react with Fe ²⁺ but used in an amount sufficient to form an OH radical, it is preferably used in an amount 300-600㎎ / ℓ for H2O2. Ions are oxidized and removed by reaction with OH-radical produced as in the following scheme.

^{_{Fe 2+ + H 2 O 2 →}} Fe 3+ + OH - + OH

^{CN - + 2OH - → CNO -} + H 2 O + 2e-

_{^{2CNO - + 4OH- → 2CO 2 +}} N 2 + 2H 2 O + 6e-

_{^{CNO - + 2H 2 O → NH}} 4 + + Co 3 2-

Thereafter, by adding a polymer flocculant and a coagulant aid, these and the remaining iron salts and cyan compounds react to form flocs. The flocs are crosslinked and adsorbed to each other to grow into larger flocs, which are easily precipitated and separated. Residual oil is also adsorbed and removed from the floc. Ca (OH) ₂ was used as the coagulant aid and polyacrylamide (PAA) was used as the polymer coagulant. The amount of the coagulant aid and the polymer coagulant is also adjusted according to the composition and concentration of the wastewater.

Hereinafter, embodiments of the present invention will be described in detail.

Example 1

As shown in FIG. 2, COG condensed water having a cyan concentration of 20-70 mg / l and an oil concentration of 700-800 mg / l was added to the first reactor, H ₂ SO ₄ was added thereto to adjust the pH to about 4, and iron salt ( FeCl ₂ ) 400-600mg / l and H ₂ O ₂ 300-600mg / l was added for oxidation for 1 hour, and then Ca (OH) ₂ and PAA were added to the secondary reactor for coagulation for at least 5 minutes. The cyan compound and oil component removal experiments were carried out, and the test results are shown in Table 1 below. As shown in Table 1 below, by adding iron salt, H ₂ O ₂ , Ca (OH) ₂ , PAA, the removal rate of cyan and oil components was very excellent, 96% and 99%, respectively.

TABLE 1

Example 2

Wastewater containing cyan compounds and oil components as in Example 1 was subjected to cyanide removal experiments according to the pH change in the first oxidation reaction step, and the results are shown in Table 2 below.

TABLE 2

As can be seen from Table 2, the cyan removal rate was the highest at 95% near pH4.

Comparative Example 1

The same COG condensate as in Example was treated by the conventional method as shown in FIG. 1 and the results are shown in Table 3 below. As can be seen from the results, even after 72 hours of aeration of the COG condensate with the initial concentration of 67 mg / l, the cyan concentration was 30 mg / l, indicating that the removal efficiency was not as high as 55%.

TABLE 3

Comparative Example 2

After performing the cyanide and oil removal experiments with the COG condensed water as in the Example with the oxidizing agent NaOCl, the results are shown in Table 4 below. As can be seen from the results, even after chemical treatment of COG condensate with cyan concentration 67 mg / ℓ oil concentration 800 mg / ℓ, the cyan concentration 17 mg / ℓ oil concentration was 64 mg / ℓ.

TABLE 4

As can be seen from the above results, the efficiency of simultaneously removing cyanide and oil is improved by treating wastewater with the method of the present invention as compared to the conventional method.

Claims (3)

In the method of treating heavy oil contained in the wastewater by gravity and then treating the homogenized COG wastewater with cyanide compounds and oil, the pH of the wastewater is adjusted to 3.5-4.5 and then ferrous salt and H ₂ O ₂ are added to OH. Generating radicals to oxidize cyan ions; And administering a polymer coagulant adjuvant Ca (OH) ₂ to the wastewater from which the cyan ions were first removed to form a floc with the residual iron salt and the cyan compound, and simultaneously adsorb the oil component to the floc to remove the cyan and the oil. Simultaneous removal method of cyan compound and oil components in wastewater containing The method according to claim 1, wherein the first iron salt is FeCl ₂ , the addition amount is characterized in that 400-600mg / L The method of claim 1, wherein the amount of H ₂ O ₂ added is 300-600 mg / L